Delivery of cardiac stimulation devices

ABSTRACT

Some embodiments of an electrical stimulation system employ wireless electrode assemblies to provide pacing therapy, defibrillation therapy, or other stimulation therapy. In certain embodiments, the wireless electrode assemblies may include a guide wire channel so that each electrode assembly can be advanced over a guide wire instrument through the endocardium. For example, a distal tip portion of a guide wire instrument can penetrate through the endocardium and into the myocardial wall of a heart chamber, and the electrode assembly may then be advanced over the guide wire and into the heart chamber wall. In such circumstances, the guide wire instrument (and other portions of the delivery system) can be retracted from the heart chamber wall, thereby leaving the electrode assembly embedded in the heart tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/476,599, filed May 21, 2012, which is a Continuation of U.S.application Ser. No. 12/910,106, filed on Oct. 22, 2010, now issued asU.S. Pat. No. 8,185,213, which is a Division of U.S. application Ser.No. 11/490,916, filed Jul. 21, 2006, now issued as U.S. Pat. No.7,840,281, the benefit of priority of each of which is claimed herein,and each of which is hereby incorporated herein by reference in itsrespective entirety.

TECHNICAL FIELD

This document relates to systems that electrically stimulate cardiac orother tissue and to systems for delivering stimulation devices.

BACKGROUND

Pacing instruments can be used to treat patients suffering from any of anumber of heart conditions, such as a reduced ability to deliversufficient amounts of blood from the heart. For example, some heartconditions may cause or be caused by conduction defects in the heart.These conduction defects may lead to irregular or ineffective heartcontractions. Cardiac pacing systems (e.g., a pacemaker or animplantable defibrillator with pacing capability) may be implanted in apatient's body so that wire electrodes in contact with the heart tissueprovide electrical stimulation to regulate electrical conduction in theheart tissue. Such regulated electrical stimulation is done to cause theheart to contract and hence pump blood.

The wired pacing systems in current use include a pulse generator thatis implanted, typically in a patient's pectoral region just under theskin. One or more wired leads extend from the pulse generator so as tocontact various portions of the heart. An electrode at a distal end of alead may provide the electrical contact to the heart for delivery of theelectrical pulses generated by the pulse generator and delivered to theelectrode through the lead.

The use of wired leads may limit the number of sites of heart tissue atwhich electrical energy may be delivered. For example, most commerciallyavailable pacing leads are not indicated for use inside the leftchambers of the heart. One reason is that the high pumping pressure inthe left chambers of the heart may cause a thrombus or clot that formson the bulky wired lead to eject into distal arteries, thereby causingstroke or other embolic injury. Thus, in order to pace the left side ofthe heart with a wired lead, most wired leads are directed through thecardiac venous system (outside the left chambers of the heart) to a sitein a cardiac vein along the exterior of the left side of the heart.

In one example of a pacing therapy that includes pacing of a left heartchamber, a treatment known as biventricular pacing may be performed whenthe left ventricle does not contract in synchrony with the rightventricle. In order to perform such pacing therapy, typically a firstwired lead is implanted through a vein into the right atrium, a secondwired lead is implanted through a vein into the right ventricle, and athird wired lead is implanted through a vein and into the coronary sinusvein (to pace the left ventricle wall from outside the left ventricle).These three wired leads may be connected to a pacemaker device (e.g.,implanted in the pectoral region) in an attempt to regulate thecontractions of the right and left ventricles.

In addition to conventional wired pacing systems, one type of pacingsystem being developed includes wireless operation. For example, somepacing systems may use wireless electrodes that are attached to theouter epicardial surface of the heart (external to the heart chambers)or embedded in a cardiac vein (external to the heart chambers) tostimulate heart tissue.

SUMMARY

Some embodiments of an electrical stimulation system employ wirelesselectrode assemblies to provide pacing therapy, defibrillation therapy,or other stimulation therapy. The wireless electrode assemblies mayreceive energy via an inductive coupling with another device outside theheart (e.g., implanted adjacent to one or more ribs) so as to provideelectrical stimulation to the nearby heart tissue. In certainembodiments, the wireless electrode assemblies may include a guide wirechannel so that each electrode assembly can be advanced over a guidewire instrument through the endocardium. For example, a distal tipportion of a guide wire instrument can penetrate through the endocardiumand into the myocardial wall of a heart chamber, and the electrodeassembly may then be advanced over the guide wire and into the heartchamber wall. In such circumstances, the guide wire instrument (andother portions of the delivery system) can be retracted from the heartchamber wall, thereby leaving the electrode assembly embedded in theheart tissue.

Some embodiments include an electrode delivery system for delivering awireless electrode assembly into a heart chamber wall. The system mayinclude a wireless electrode assembly including a body that defines aguide wire channel extending therethrough. The system may also include adelivery catheter to direct the wireless electrode assembly through aheart chamber and toward a heart chamber wall. The delivery catheter mayhave a distal opening through which the wireless electrode assembly ispassable for delivery into the heart chamber wall. The system mayfurther include a guide wire instrument passable through the deliverycatheter to penetrate into the heart chamber wall. The guide wireinstrument may have a distal tip portion that is slidable within theguide wire channel of the wireless electrode assembly when the wirelesselectrode assembly is advanced over the guide wire instrument into theheart chamber wall.

In particular embodiments, an electrode delivery system for delivering awireless electrode assembly may include a delivery catheter to direct awireless electrode assembly toward a heart chamber wall when theelectrode assembly is disposed therein. The delivery catheter may have adistal opening through which the wireless electrode assembly ispassable. The system may also include an actuation member to push theelectrode assembly out of the distal opening of the delivery catheterand into the heart chamber wall. The actuation member may be movablyadjustable within the delivery catheter. Further, the system may includea guide wire instrument passable through the delivery catheter andhaving a distal tip portion to define a penetration path throughendocardium tissue and into myocardium tissue of the heart wall chamber.When the actuation member pushes the electrode assembly out of thedistal opening of the delivery catheter, the electrode assembly advancesover the distal tip portion of the guide wire instrument to implant intothe myocardium tissue along the penetration path.

In some embodiments, a wireless electrode assembly for electricalstimulation of heart tissue may include a body portion at leastpartially containing a circuit to deliver electrical stimulation from anelectrode surface. The assembly may also include a tissue penetrationsurface along the body portion to initiate penetration of the bodyportion into a heart chamber wall. The assembly may further include aguide wire channel defined by the body portion and extending in alongitudinal direction through the body portion toward the tissuepenetration surface.

Some embodiments include a method for delivering a wireless electrodeassembly into a heart chamber wall. The method may include directing adistal portion of a delivery catheter into a heart chamber, andadvancing a guide wire instrument out of the distal portion of thedelivery catheter to penetrate a distal tip portion of guide wireinstrument into a heart chamber wall. The method may also includeadvancing a wireless electrode assembly out of the distal portion of thedelivery catheter and over the distal tip portion of the guide wireinstrument to implant the electrode assembly in the heart chamber wall.

Some of the embodiments described herein may have one or more of thefollowing advantages. First, the delivery system may include a guidewire instrument that initiates penetration of the heart chamber wall,thereby facilitating the subsequent penetration by the electrodeassembly. Second, the guide wire instrument may include one or moresensor electrodes to sense local electrical activity (e.g., anelectrogram or the like) and to transmit a test stimulation signal(e.g., a pacing signal) at the proposed implantation site. Third, thedelivery system may be configured to advance the electrode assembly in acontrolled manner to a selected insertion depth into the heart walltissue. Fourth, the delivery system may include a magnetic couplingdevice that releasably retains the electrode assembly in a deliverycatheter. Fifth, the delivery system may include a guide wire instrumentthat is configured to guide the electrode assembly into the heart walltissue along a curved insertion path, thereby permitting the electrodeassembly to be embedded between selected tissue fibers. Sixth, thedelivery system may include a guide wire instrument having one or morefixation devices extending therefrom so as to secure the guide wireinstrument to the heart wall tissue and maintain the guide wire positionduring the implantation process. Seventh, the delivery system mayinclude a guide wire instrument having a detachable tip portion thatserves to reduce migration and to maintain the orientation of theelectrode assembly implanted in the heart wall tissue. Eighth, thedelivery system may include a delivery catheter that is releasablyattachable to the heart chamber wall so as to maintain the position ofthe delivery catheter during the implantation process.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a section view of a heart and at least a portion of anelectrode delivery system, in accordance with some embodiments.

FIG. 2 is a partial cross-sectional view of the portion of the electrodedelivery system of FIG. 1.

FIG. 3 is a perspective view of the electrode delivery system of FIG. 1and an electrical stimulation system, in accordance with someembodiments.

FIG. 4 is a diagram of a device of the electrical stimulation system ofFIG. 3.

FIG. 5 is a circuit diagram of at least a portion of a wirelesselectrode assembly of the electrical stimulation system of FIG. 3.

FIGS. 6-8 are partial cross-sectional views of an electrode deliverysystem, in accordance with some embodiments.

FIGS. 9-10 are partial cross-sectional views of another embodiment of anelectrode delivery system.

FIGS. 11-15 are perspective views of portions of guide wire instruments,in accordance with some embodiments.

FIG. 16 is a partial cross-sectional view of an electrode deliverysystem having a detachable guide wire portion, in accordance with someembodiments.

FIG. 17 is a partial cross-sectional view of another embodiment of anelectrode delivery system having a detachable guide wire portion.

FIGS. 18-19 are partial cross-sectional views of an electrode deliverysystem having a detachable anchor portion, in accordance with someembodiments.

FIG. 20 is a partial cross-sectional view of an electrode deliverysystem having a detachable guide wire portion, in accordance with someembodiments.

FIG. 21 is a side view of a portion of an electrode delivery system, inaccordance with some embodiments.

FIGS. 22-25 are views of portion of electrode delivery system, inaccordance with some embodiments.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1, an electrode delivery system 100 may be used tointroduce one or more wireless electrode assemblies 120 into the heartchamber walls. In this example, there are four wireless electrodeassemblies 120 implanted in the heart chamber wall of each of the leftatrium 32, the left ventricle 34, the right atrium 36, and the rightventricle 38. As described below in connection with FIGS. 3-5, thewireless electrode assemblies 120 may be part of an electricalstimulation system 20 that wirelessly transmits energy to the electrodeassemblies 120 for electrical stimulation of the surrounding heart walltissue 35. The electrode delivery system 100 includes a deliverycatheter 130 with a distal opening and a guide wire instrument 140 thatis passable through the delivery catheter 130. The guide wire instrument140 is capable of penetrating into a heart chamber wall, as shown inFIG. 1. After penetration, an electrode assembly 120 is advanced in adistal direction over at least a portion of the guide wire instrument140 so that the electrode assembly 120 is implanted entirely within theheart chamber wall, as shown in FIG. 1. Exemplary embodiments of theproximal portions of the delivery catheter 130 and the guide wire 140extending outside the patient's body are shown and described below inconnection with FIG. 3.

In more detail, the delivery system 100 shown in FIG. 1 includes a guidesheath 110 that is capable of being directed (e.g., by a surgeon orother user) through one or more veins or arteries to the targetedchamber of the heart 30 (e.g., the left ventricle 34 is the targetedchamber in the embodiment shown in FIG. 1). For example, in thoseembodiments in which the atrial septum or a heart valve is to be crossedduring the delivery procedure, the guide sheath 110 can maintain such acrossing while a plurality of electrode assemblies 120 are directedtherethrough into the targeted heart chamber. For example, in theembodiment shown in FIG. 1, the guide sheath 110 maintains a crossingthrough the atrial septum (e.g., entering through the right atrium 36,passing through the atrial septum, and passing into the left atrium 32)and maintain a crossing through the left mitral valve (e.g., passingthrough the left mitral valve, and passing into the left ventricle 34).In an alternative example, the guide sheath 110 can be directed througha femoral artery, around the aortic arch, and into the left ventricle34.

After the guide sheath 110 is deployed into the targeted heart chamber,multiple wireless electrode assemblies 120 may be consecutivelydelivered through the guide sheath 110 using at least one deliverycatheter 130. The multiple assemblies 120 may be delivered withouthaving to remove the outer sheath 110, thereby reducing the deliverytime and reducing the likelihood of trauma to the atrial septum or heartvalve crossing due to repeated insertions.

Still referring to FIG. 1, the guide wire instrument 140 has a distaltip adapted to penetrate through the endocardium 33 and into the heartwall tissue 35 (e.g., tissue such as the myocardial wall) before theelectrode assembly 120 is advanced into the heart wall tissue 35. Assuch, the guide wire instrument 140 may initiate a penetration path intothe heart chamber wall, thereby facilitating the subsequent penetrationby the electrode assembly 120 along the penetration path. For example,in the embodiment depicted in FIG. 1, the distal tip portion 142 of theguide wire instrument 140 can penetrate through the endocardium 33 andinto the heart wall tissue 35, thereby forming an opening in theendocardium 33. Then the electrode assembly 120 can be advanced over thedistal tip portion 142 to further dilate opening in the endocardium 33(which was previously formed by the guide wire instrument 140) and topenetrate into the heart wall tissue 35.

In addition, the guide wire instrument 140 may include at least onesensor electrode 144 (FIG. 2) along its distal tip portion 142 that isconfigured to sense local electrical activity (e.g., an electrogram orthe like) and to transmit a test stimulation signal (e.g., a pacingsignal) after initiating the penetration into the implantation site. Inthese circumstances, the guide wire instrument 140 may be used todetermine if the implantation site is suitable for receipt of anelectrode assembly 120 before the electrode assembly 120 is advancedinto the heart wall tissue 35. For example, the guide wire instrument140 may comprise a conductive electrical line extending from the sensorelectrode 144 (FIG. 2) along the distal tip portion 142 to the proximalportion 148 (FIG. 3) of the guide wire instrument 140 (e.g., outside thepatient's body). In these circumstances, the guide wire instrument 140may be connected to an electrogram or ECG monitor system or the like sothat a physician may view the local electrical activity in the heartwall tissue 35 into which the distal tip portion 142 has penetrated.Further, a pulse generator device or the like may be electricallyconnected to the proximal portion 148 (FIG. 3) of the guide wireinstrument 140 (e.g., outside the patient's body) so as to transmit testpacing signals to heart wall tissue 35 adjacent to the distal tipportion 142. In some circumstances, the sensor electrode 144 maycomprise a marker material that permits viewability of the guide wireinstrument 140 in the heart 30 using medical imaging techniques. Inaddition or in the alternative, at least the distal tip portion 142 ofthe guide wire instrument 140 may comprise a marker material or a markerband (not shown) to permit viewability of the guide wire instrument 140in the heart 30 using medical imaging techniques.

FIG. 2 shows a more detailed view of the distal portion of theembodiments of the delivery system 100 and the wireless electrodeassembly 120 previously described in connection with FIG. 1. Theelectrode assembly 120, in this example, includes a guide wire channel122 through which at least a distal tip portion 142 of the guide wireinstrument 140 extends. A movable engagement between the electrodeassembly 120 and the guide wire instrument 140 (e.g., a slidableengagement) permits the electrode assembly 120 to be advanced over theguide wire instrument 140 into the heart wall tissue 35 and permits theguide wire instrument 140 (and other portions of the delivery system100) to be retracted from the electrode assembly 120 after implantationis completed. In this embodiment, the electrode assembly 120 alsoincludes a body portion 125 that at least partially contains a circuit(described in more detail below in connection with FIG. 5) to deliverelectrical stimulation from one or more electrode surfaces 124 and 126.For example, in those embodiments in which the electrode assembly 120provides bipolar functionality, the electrode assembly 120 may include afirst electrode 124 disposed opposite a second electrode 126 so as toprovide a stimulation circuit from one electrode (e.g., the secondelectrode 126), through the surrounding heart wall tissue 35, and to theother electrode (e.g., the first electrode 124). As shown in FIG. 2, thefirst and second electrodes 124 and 126 may be disposed along an outersurface of the body portion 125 so as to contact the heart wall tissue35 when implanted therein. The electrode assembly 120 may also include atissue penetration surface 127 along the body portion 125 to facilitatepenetration of the body portion 125 into the heart wall tissue 35. Forexample, the tissue penetration surface 127 has a generally conicalshape or other distally narrowing shape to facilitate the insertionprocess. In the embodiment depicted in FIG. 2, the distal electrode 126extends along the conical surface of the tissue penetration surface 127.The guide wire channel 122 may extend in a substantially longitudinaldirection through the body portion 125 toward the tissue penetrationsurface 127 so that the tissue penetration surface 127 can be advancedin the direction of the previously inserted guide wire instrument 140.As previously described, in this embodiment, the guide wire instrument140 includes at least one sensor electrode 144 disposed along the distaltip portion 142 to sense local electrical activity (e.g., an electrogramor the like) and to transmit a test stimulation signal (e.g., a pacingsignal).

In some embodiments, the wireless electrode assemblies 120 may be sizedto be implanted entirely within a heart chamber wall, which can have awall thickness of about 3 mm to about 30 mm and more specifically about5 mm to about 25 mm for ventricle walls, and about 1 mm to about 5 mmand more specifically about 2 mm to about 4 mm for atrial walls. Also inthese embodiments, the wireless electrode assemblies 120 are sized toslidably receive at least the distal tip portion 142 of the guide wireinstrument 140, which can have an outer diameter of about 0.1 mm toabout 1.0 mm, about 0.2 mm to about 0.8 mm, and more specifically about0.25 mm to about 0.5 mm. Accordingly, in such embodiments, the bodyportion 125 of the electrode assembly 120 may have a longitudinal lengthof about 20 mm or less, about 15 mm or less, about 10 mm or less, forexample, about 3 mm to about 10 mm, and in some circumstances (e.g.,implantation in the atrial wall) about 5 mm or less, for example about 3mm to about 5 mm. Also, in these embodiments, the body portion 125 mayhave a generally circular cross-sectional shape with a maximum outerdiameter of about 0.5 mm to about 3.5 mm, about 1 mm to about 3 mm, andmore specifically about 1.5 mm to about 2.5 mm. Further, in someembodiments, the guide wire channel 122 may have a diameter of about0.15 mm to about 1.05 mm, about 0.25 mm to about 0.85 mm, and about 0.30mm to about 0.55 mm so as to accommodate the guide wire instrument 140having a diameter as previously described.

Still referring to FIG. 2, the electrode assembly 120 may be releasablyretained in the distal portion 134 of the delivery catheter 130 duringadvancement through the guide sheath 110. In this embodiment, a magneticcoupling device 150 is disposed in the distal portion 134 of thedelivery catheter 130 so as to releasably retain the electrode assembly120 in a non-deployed position (not shown in FIG. 2). For example, themagnetic coupling device 150 may include one or more ring magnetsaxially aligned with the distal portion 134 of the delivery catheter 130so that a distal surface 158 of the magnetic coupling device 150 ismagnetically attracted to an opposing surface 128 of the electrodeassembly 120. In this embodiment, the magnetic coupling device 150comprises rare earth magnets and the proximal surface 128 of theelectrode assembly 120 may comprise a magnetically attractable metalmaterial, such as stainless steel or the like. In some circumstances,the magnetic coupling device 150 disposed in the distal portion 134 ofthe delivery catheter 130 may aid in controlled-delivery of the deliverycatheter through the patient's body and into the targeted heart chamber.For example, the magnetic coupling device 150 in the distal portion ofthe delivery catheter 130 can be directed through the patient's venousor arterial system using a magnetic navigation system, in which two ormore large magnets outside the patient's body are arranged to generatemagnetic fields that direct the distal portion 134 of the catheter 130 Ithe desired direction. One example of such a magnetic navigation systemsupplied by Stereotaxis, Inc. of St. Louis, Mo.

Alternatively, the magnetic coupling device 150 comprises a coil of wirewound around a permeable core such as iron or ferrite, so that whencurrent flows through said coil, device 150 is magnetically attracted toproximal surface 128, and when the coil current is switched off, device150 releases from proximal surface 128. The current in said coil may beeither direct or alternating current (DC or AC). In those embodiments inwhich the current for providing electromagnetic attraction to proximalsurface 128 is AC, the magnetic coupling device 150 may provide amagnetic field that inductively couples with the coil in the electrodeassembly 120 to provide a supplemental recharge to the electrodeassembly 120 during the delivery process. Such a supplemental rechargefrom the magnetic coupling device 150 may ensure that there issufficient energy stored for a test stimulation pulse (described in moredetail below in connection with FIGS. 6-8) between the electrodes 124and 126 during the implantation of the electrode assembly 120 (e.g., toverify the operation of the electrode assembly in the implantationsite).

It should be understood that, in other embodiments, the electrodeassembly 120 may be releasably retained in the delivery catheter 130using a friction-fit engagement, a mechanical connection (e.g., athreaded engagement, a mating slot and groove engagement, etc.), or thelike.

As shown in FIG. 2, an actuation member 160 may be adjusted within thedelivery catheter 130 to release the electrode assembly 120 from thedistal portion 134 of the delivery catheter 130. For example, after thedelivery catheter 130 is directed to a position adjacent to a targetedheart chamber wall, the actuation member 160 may be adjusted to forcethe electrode assembly 120 away from the magnetic coupling device 150and into the heart wall tissue 35 that was previously penetrated by theguide wire instrument 140. In this embodiment, the actuation member 160serves as an adjustable push rod that can shift from a retractedconfiguration to an extended configuration so as to advance theelectrode assembly 120 to a deployed position outside the distal opening135 of the delivery catheter 130. The actuation member 160 may comprisea flexible main shaft 163 that can transmit a pushing force applied fromthe proximal end (e.g., outside the patient's body) to a distal section162. As described in more detail below in connection with FIG. 3, asurgeon or other user can actuate a hand-operated trigger device 137 orthe like disposed along the proximal portion 138 of the deliverycatheter 130 to apply the pushing force to the actuation member 160 andthereby adjust the position of the distal section 162. The distalsection 162 may have a reduced diameter that is advanced through acentering mechanism 154 so as to abut the proximal surface 128 of theelectrode assembly 120 during advancement of the electrode assembly 120over the guide wire instrument 140. The distal section 162 maytransition to the reduced diameter at a shoulder 164, which isconfigured to abut the centering mechanism 154 when the actuation member160 has been advanced to a predetermined extension distance (refer, forexample, to distance L in FIG. 6). As such, the actuation member 160 maybe used to advance the electrode assembly 120 to a selected depth intothe hearth wall tissue 35, and such advancement may cease when theshoulder 164 of the actuation member 160 abuts with the centeringmechanism 154. Accordingly, the heart wall tissue 35 can be protectedfrom over advancement of the electrode assembly, which could result inthe electrode assembly 120 being forced entirely through the heart wall.

In an alternative embodiment, the magnetic coupling device 150 and thecentering mechanism 154 may be incorporated onto the main shaft 163 ofthe actuation member 160. In such circumstances, the distal section 162would be an inner push rod shaft that extends fully through the mainshaft of the actuation member 160. Thus, the actuation member 160, themagnetic coupling 150, and the electrode assembly 120 may be insertedinto a proximal portion 138 of the delivery catheter 130 (e.g., outsidethe patient's body as shown in FIG. 3) and directed through the deliverycatheter 130 to the targeted implantation site. In these embodiments,when the electrode assembly 120 is to be released from the magneticcoupling device 150, the distal section 162 can be moved distallyrelative to the main shaft 163.

Referring to FIGS. 2-3 (showing the distal portion and proximal portionof the delivery system 100, respectively), during a surgical processconducted by a surgeon or other user, the electrode assembly 120 may bedisposed in the delivery catheter 130 and advanced through the guidesheath 110 toward the targeted heart chamber 32, 34, 36, or 38. As shownin FIG. 3, the guide sheath 110 may be introduced via an incision in thepatient's neck and advanced through the venous system to the heart 30(e.g., though the superior vena cava, through the right atrium 36,crossing through the atrial septum, through the left atrium 32, and intothe left ventricle 34). As shown in FIG. 2, the guide sheath 110 may beconfigured to slidably receive the delivery catheter 130 so that theelectrode assembly 120 may be loaded into the delivery catheter 130outside the patient's body and then directed through the guide sheath110 to the heart 30. For example, before the distal end of the deliverycatheter 130 is inserted into the proximal portion 118 of the guidesheath 110 (refer to FIG. 3 for an exemplary embodiment of the proximalportion 118), the user may insert the electrode assembly 120 into thedistal opening 135 of the delivery catheter 130 and force the electrodeassembly 120 toward a releasably retainer device (e.g., the magneticcoupling device 150 as described in connection with FIG. 2). Then thedelivery catheter 130 (with the electrode assembly 120 retained therein)can be inserted into the proximal portion 118 of the guide sheath 110and directed therethrough to the targeted heart chamber. The user caninsert the guide wire instrument 140 into the proximal portion 138 ofthe delivery catheter 130 (refer to FIG. 3 for an exemplary embodimentof the proximal portion 138) and advance the guide wire instrument 140therethrough to penetrate the targeted tissue site within the targetedheart chamber. As shown in FIG. 3, the surgeon or other user may operatethe trigger device 137 along the proximal portion of the deliverycatheter 130 to adjust the distal section 162 of the actuation member160 (FIG. 2). The actuation member 160 forces the electrode assembly 120to deployed out of the distal opening 135 of the delivery catheter 130and over the distal tip portion 142 for implantation into the heart walltissue 35. After the electrode assembly 120 is implanted in the heartwall tissue 35, the delivery catheter 130 and the guide wire instrument140 may be withdrawn from the proximal portion 118 of the guide sheath110 (e.g., withdrawn fully outside of the patient's body), while theguide sheath 110 remains in the patient's body, for example, to maintainthe delivery path into the targeted heart chamber. If a subsequentelectrode assembly is to be delivery to the same heart chamber, a newelectrode assembly 120 may be loaded into the distal opening 135 of samedelivery catheter 130 (or into a new delivery catheter 130 having asimilar construction) for delivery through the guide sheath 110 to a newimplantation site along the targeted heart chamber wall.

In these embodiments, the guide sheath 110 can include a steeringmechanism (not shown in FIGS. 2-3), such as steering wires, shape memorydevice, or the like, to shift the distal end during advancement into thetargeted heart chamber and optionally includes at least one marker band112 (FIG. 2) to permit viewability of the distal end of the guide sheath110 in the patient's body using medical imaging techniques. Such amarker band 112 may aid a physician when steering the guide sheath 110to the targeted heart chamber. Likewise, the delivery catheter 130 mayalso include a steering mechanism (not shown in FIGS. 2-3) so as toadjust its distal end during advance to a position adjacent the heartchamber wall and may also include at least one marker band 132 (FIG. 2)to permit viewability of the distal end of the delivery catheter 130 inthe patient's body using medical imaging techniques.

Referring now to the operation of the electrical stimulation system 20as shown, for example, in FIGS. 3-5, the wireless electrode assemblies120 may be part of an electrical stimulation system 20 that wirelesslytransmits energy to the electrode assemblies 120 for electricalstimulation of the surrounding heart wall tissue 35. As described inmore detail below in connection with FIG. 5, each of the wirelesselectrode assemblies 120 may have an internal coil that is inductivelycoupled with an external power source coil to charge an electricalcharge storage device (e.g., a capacitor or a battery) contained withinthe wireless electrode assembly 120. Also as described in more detailbelow, each of the wireless electrode assemblies 120 may have controlcircuitry or a triggering mechanism to deliver stored electrical chargeto adjacent heart tissue. In alternative embodiments, one or more of thewireless electrode assemblies 120 has no energy storage device, such asa battery or capacitor. In these alternative embodiments, each wirelesselectrode assembly may comprise, for example, of a ferrite core and ringelectrodes (e.g., bipolar electrodes) encircling the ends of the core. Anumber of turns of fine insulated wire may be coiled around the centralportion of the core so as to receive energy from a magnetic fieldproduced by a shaped driving signal, which causes the an stimulationpulse to pass from the coil and to the bipolar electrodes for electricalstimulation of the surrounding heart tissue.

Referring to FIG. 3, the electrical stimulation system 20 may include astimulation controller 40 (e.g., a pacing controller) and a transmitter50 that drives an antenna 60 for communication with the wirelesselectrode assemblies 120. The stimulation controller 40 can includecircuitry to sense and analyze the heart's electrical activity, and todetermine if and when a stimulation electrical pulse needs to bedelivered and by which of the wireless electrode assemblies 120. Thesensing capability may be made possible by having sensor electrodesincluded within the physical assembly of the stimulation controller 40.Alternatively, a single or dual lead pacemaker 90 may sense the localcardiac electrogram and transmit this information to the antenna 60 foruse by the controller 40 in determining the timing of wireless electrodeassembly 120 firing. In either case, the wireless electrode assembly 120need not be provided with sensing capability, and also the wirelesselectrode assemblies 120 need not be equipped with the capability ofcommunicating to the stimulation controller 40 (for example, tocommunicate information about sensed electrical events). In alternativeembodiments, the wireless electrode assemblies 120 include local sensorcircuitry to sense the local electrical activity, such as anelectrogram. In these alternative embodiments, the local sensorcircuitry would communicate with programmable control circuitry in thewireless electrode assembly, which would wirelessly communicate thesensed information to the controller 40 or to another implantedelectrode assembly 120.

The transmitter 50—which can be in communication with, and controlledby, the stimulation controller 40—may drive an RF signal onto theantenna 60. In one embodiment, the transmitter 50 provides both (1) acharging signal to charge the electrical charge storage devices (e.g.,rechargeable battery, capacitor, or the like) contained within thewireless electrode assemblies 120 via inductive coupling, and (2) aninformation signal, such as a pacing trigger signal, that iscommunicated to a selected one or more of the wireless electrodeassemblies 120, commanding the selected wireless electrode assembly 120to deliver its stored charge to the adjacent tissue. The magnetic fieldtransmitted from the antenna 60 may be used to inductively couple with acoil in each of the electrode assemblies 120.

Still referring to FIG. 3, the stimulation controller 40 and thetransmitter 50 may be housed in a single enclosure that is implantablewithin a patient. In such a configuration, the single enclosure device25 may have a single energy source (e.g., battery) that may be eitherrechargeable or non-rechargeable. For example, as shown in FIG. 3, thestimulation controller 40 and the transmitter 50 are housed in anenclosure device 25 that is implantable along or along one or more ribsproximate to the heart 30. Such proximity between the antenna 60 and theheart 30 may facilitate efficient inductive coupling between theimplanted antenna device 60 and the wireless electrode assemblies 120embedded in the heart wall tissue 35. Accordingly, in this embodiment,the controller 40 and transmitter 50 are housed in the device 25 that isshaped generally elongate and slightly curved so that it may be anchoredbetween two ribs of the patient, or possibly around one or more ribs. Inone example, the housing for the controller 40 and transmitter 50 can beabout 2 to 20 cm long and about 1 to 5 cm in diameter, or morespecifically, can be about 5 to 10 cm long and about 1 to 2 cm indiameter. Also in this example, this rib-mounted housing may have anon-uniform cross-sectional shape to conform to the ribs and may becurved along its length. Such a shape of the housing for the controller40 and transmitter 50, which allows the device to be anchored on theribs, may provide an enclosure that is larger than conventionalpacemakers, thereby providing more space for a larger battery havingmore stored energy. In some embodiments, the controller 40 may comprisea defibrillator circuit that discharges energy to the heart 30 throughelectrodes on opposing ends of the body of controller housing 25 whenfibrillation is sensed. Other sizes and configurations may also beemployed as is practical.

In some embodiments, the antenna 60 may be a loop antenna comprised of along wire that is electrically connected across an electronic circuitcontained within the controller/transmitter housing device 25. Theelectronic circuit delivers pulses of RF current to the antenna 60,generating a magnetic field in the space around the antenna 60 to chargethe wireless electrode assemblies 120, as well as RF control magneticfield signals to command the wireless electrode assemblies 120 todischarge. In such embodiments, the antenna 60 may comprise a flexibleconductive material so that it may be manipulated by a physician duringimplantation into a configuration that achieves optimum inductivecoupling between the antenna 60 and the coils within the implantedwireless electrode assemblies 120. In one example, the loop antenna 60may be about 2 to 22 cm long and about 1 to 11 cm wide, and may be about5 to 11 cm long and about 3 to 7 cm wide. Placement of the antenna 60over the ribs may provide a relatively large antenna to be constructedthat has improved efficiency in coupling RF energy to the pacingwireless electrode assemblies 120.

In an alternative configuration, the stimulation controller 40 and thetransmitter 50 may be physically separate components. As an example ofsuch a configuration, the stimulation controller 50 may be implantable,for example in the pacemaker configuration, whereas the transmitter 50(along with the antenna 60) may be adapted to be worn externally, suchas in a harness that is worn by the patient. In the latter example, thestimulation controller 40 would have its own energy source (e.g.,battery), and that energy need not be rechargeable given the relativelysmall energy requirements of the stimulation controller 40 as comparedto the energy requirements of the transmitter 50 to be able toelectrically charge the wireless electrode assemblies 120. In this case,the stimulation controller 40 would sense the local electrogram signalthrough a wired pacing lead, and transmit the sensed information to theexternal controller. Again, transmission of information, as opposed topacing energy, has a relatively low power requirement, so a pacemakerenclosure and battery may suffice.

In some embodiments, an external programmer 70 is used to communicatewith the stimulation controller 40, including after the stimulationcontroller 40 has been implanted. The external programmer 70 may be usedto program such parameters as the timing of stimulation pulses inrelation to certain sensed electrical activity of the heart, the energylevel of stimulation pulses, the duration of stimulation pulse (that is,pulse width), etc. The programmer 70 includes an antenna 75 tocommunicate with the stimulation controller 40, using, for example, RFsignals. The implantable stimulation controller 40 is accordinglyequipped to communicate with the external programmer 70, using, forexample, RF signals. The antenna 60 may be used to provide suchcommunications, or alternatively, the stimulation controller 40 may havean additional antenna (not shown in FIG. 3) for external communicationswith the programmer 70, and in an embodiment where the transmitter 50and antenna 60 are housed separately from the controller 40, forcommunications with the transmitter 50.

As shown in FIG. 3, some embodiments of the system 20 may also include apacemaker/defibrillator device 90 and associated wired leads 95 whichextend from the pacemaker/defibrillator device 90 and into one or morechambers of the heart 30. For example, the system 20 may include wiredleads 95 from the pacemaker/defibrillator 90 that extend into the rightatrium 36 and the right ventricle 38 while wireless electrode assembliesare disposed in the left atrium 32 and the left ventricle 34. Thepacemaker/defibrillator 90 may be used to sense the internal electrogramor ECG signals, to deliver defibrillation shocks, and to communicatewith the controller 40 and/or transmitter 50 as previously described.

One parameter of the wireless electrode assembly 120 that may be afactor in the design of the electrical stimulation system 20 is thestimulation energy required to pace or otherwise stimulate theventricles 34 and 38 or other chamber of the heart 30. This energyrequirement can include a typical value needed to pace ventricularmyocardium, but also can include a margin to account for degradation ofcontact between the electrodes and tissue over time. In certainembodiments, each wireless electrode assembly 120 may require themaximum pacing threshold energy. This threshold energy is supplied tothe wireless electrode assemblies between heartbeats by an externalradio frequency generator (which may also be implanted), or othersuitable energy source that may be implanted within the body or from arechargeable battery contained within electrode assembly 120. In somecircumstances, parameter values for some embodiments may be:

-   -   Threshold pacing voltage=2.5 Volts    -   Approximate tissue impedance=600 Ohms    -   Approximate pulse duration=0.4 mSec    -   Derived threshold energy=4 micro-Joules

Because RF fields at frequencies higher than about 200 kHz may beattenuated by the body's electrical conductivity, and because electricfields of any frequency may be attenuated within the body, energytransmission through the body may be accomplished in some embodimentsvia a magnetic field at about 20-200 kHz (or by a magnetic field pulsethat contains major frequency components in this range), and moreparticularly by transmission of magnetic fields in the range of 100-200kHz when transmission is through relatively conductive blood and heartmuscle.

In some embodiments, each of the wireless electrode assemblies 120includes a rechargeable battery. This battery may provide power fordelivering pacing energy to the tissue, and for operatingcommunications, logic, and memory circuitry contained within theassembly. In such embodiments, the transmitter 50 and the antenna 60(FIG. 3) may be external to the patient, and may serve to recharge thebatteries within the electrode assemblies. The recharge transmitter andantenna may be incorporated into furniture, incorporated into thepatient's bed, or worn by the patient (e.g., in a vest-type garment).Daily recharging for predetermined periods (e.g., about 30 minutes) maybe required. In these circumstances, the wireless electrode assemblies120 may be autonomous pacing devices, which can sense the localelectrogram and only pace when the local tissue is not refractory. Suchelectrodes may communicate with the programming unit 70 to receivepacing instructions and transmit data stored in local memory. In theseembodiments, each wireless electrode assembly 120 may also communicatewith other implanted wireless electrode assemblies 120. For example, oneelectrode assembly 120 in the right atrium may be designated as the“master,” and all other implanted electrodes are “slaves” that pace withpre-programmed delays relative to the “master.” As such, a masterelectrode in the right atrium may only sense the heart's sinus rhythm,and may trigger pacing of the slaves with programmed delays.

Referring to FIG. 4, an embodiment of an implantable device 25 (e.g.,the rib-implanted configuration shown in FIG. 3) including thecontroller 40, transmitter 50, and associated antenna 60 is shown inblock diagram form. Included within the device 25 is: a battery 26,which may be recharged by receiving RF energy from a source outside thebody via antenna 60; ECG sensing electrodes 27 and associated sensingcircuitry 28; transmitter circuitry 50 for transmitting RF energy andfiring commands to the implanted wireless electrode assemblies,transmitting status information to the external programmer, receivingcontrol instructions from the external programmer, and receiving powerto recharge the battery; and a stimulation controller 40 that isprogrammed to control the overall functioning of the implantable device25. In alternative embodiments, antenna 60 may receive signals from theindividual wireless electrode assemblies 120 containing informationregarding the local electrogram at the site of each wireless electrodeassembly, and/or the antenna 60 may receive signals from an implantedpacemaker device 90 regarding the electrogram signal at the sites of oneor more conventional leads implanted on the right side of the heart.

Referring to FIG. 5, some embodiments of a wireless electrode assembly120 may include a receiver coil 172 that is capable of being inductivelycoupled to a magnetic field source generating a time-varying magneticfield at the location of coil 172, such as would be generated by thetransmitter 50 and the antenna 60 depicted in FIG. 3. The RF current inthe external antenna may be a pulsed alternating current (AC) or apulsed DC current, and thus the current induced through the receivercoil 172 may likewise be an AC or pulsed DC current. The current inducedin coil 172 may be proportional to the time rate of change of themagnetic field generated at the site of coil 172 by the external RFcurrent source. In some embodiments, a four-diode bridge rectifier 173may connected across the receiver coil 172 to rectify the AC or pulsedDC current that is induced in the receiver coil 172. A three-positionswitch device 174 may be connected so that when the switch device 174 isin a first position, the rectifier 173 produces a rectified output thatis imposed across a capacitor 175 or other power storage device. Assuch, when the switch device 174 is in the position 1 (as is the case inFIG. 5), the capacitor 175 stores the induced electrical energy.

The switch device 174, in this example, can be a voltage-controlleddevice that is connected to sense a voltage across the capacitor 175 todetermine when the capacitor 175 has been sufficiently charged to aspecified pacing threshold voltage level. When the capacitor 175 issensed to have reached the specified pacing threshold level, thevoltage-controlled switch device 174 moves to a position 2, whichdisconnects the capacitor 175 from the coil 172. With the switch device174 in the position 2, the capacitor 175 is electrically isolated andremains charged, and thus is ready to be discharged. The voltagecontrolled switch device 174 may comprise a solid state switch, such asa field effect transistor, with its gate connected to the output of avoltage comparator that compares the voltage on capacitor 175 to areference voltage. The reference voltage may be set at the factory, oradjusted remotely (e.g., after being implanted) via signals sent fromthe physician programmer unit 70 (FIG. 3), received by coil 172 andprocessed by circuitry not shown in FIG. 5. The electronic circuitrycontained within the wireless electrode assembly 120, including thevoltage controlled switch 174, can be constructed with components thatconsume very little power, for example CMOS. Power for such circuitry iseither taken from a micro-battery contained within the wirelesselectrode assembly, or supplied by draining a small amount of chargefrom capacitor 175.

Still referring to FIG. 5, a narrow band pass filter device 176 may alsobe connected across the receiver coil 172, as well as being connected tothe three-position switch device 174. The band pass filter device 176passes only a single frequency of communication signal that is inducedin the coil 172. The single frequency of the communication signal thatis passed by the filter device 176 may be unique for the particularwireless electrode assembly 120 as compared to other implanted wirelesselectrode assemblies. When the receiver coil 172 receives a shortmagnetic field burst at this particular frequency, the filter device 176passes the voltage to the switch device 174, which in turn moves to aposition 3. With the switch device 174 in the position 3, the capacitor175 may be connected in series through the previously describedelectrodes 124 and 126 (refer also to FIG. 2), to the tissue to bestimulated. As such, at least some of the charge that is stored on thecapacitor 175 is discharged through the tissue (e.g., heart wall tissue35). When this happens, the tissue becomes electrically depolarized. Inone example embodiment described in more detail below, the bipolarelectrodes 124 and 126 across which stimulation pulses are provided arephysically located at opposite ends (e.g., a proximal end and a distalend) of the wireless electrode assembly 120. After a predetermined, orprogrammed, period of time, the switch returns to position 1 so thecapacitor 175 may be charged back up to the selected threshold level.

It should be noted that, for sake of clarity, the schematic diagram ofFIG. 5 shows only the electrical components for energy storage and forswitching, in accordance with particular embodiments of the wirelesselectrode assembly 120. Not necessarily shown are electronics tocondition the stimulation pulse delivered to the tissues, whichcircuitry should be understood from the description herein. Some aspectsof the pulse, for example pulse width and amplitude, may be remotelyprogrammable via encoded signals received through the filter device 176of the wireless electrode assembly 120. In this regard, filter 176 maybe a simple band pass filter with a frequency unique to a particularwireless electrode assembly, and the incoming signal may be modulatedwith programming information. Alternatively, filter 176 may consist ofany type of demodulator or decoder that receives analog or digitalinformation induced by the external source in coil 172. The receivedinformation may contain a code unique to each wireless electrodeassembly to command discharge of capacitor 175, along with moreelaborate instructions controlling discharge parameters such asthreshold voltage for firing, duration and shape of the discharge pulse,etc.

Using wireless electrode assemblies 120 of the type shown in FIG. 5, allof the implanted wireless electrode assemblies 120 may be chargedsimultaneously by a single burst of an RF charging field from atransmitter antenna 60. Because back reaction of the wireless electrodeassemblies 120 on the antenna 60 may be small, transmitter 50 (FIG. 3)losses may be primarily due to Ohmic heating of the transmit antenna 60during the transmit burst, Ohmic heating of the receive coil 122, andOhmic heating of conductive body tissues by eddy currents induced inthese tissues by the applied RF magnetic field. By way of comparison, ifeight wireless electrode assemblies 120 are implanted and each isaddressed independently for charging, the transmitter 50 may be turnedON eight times as long, which may require almost eight times moreenergy, the additional energy being primarily lost in heating of thetransmit antenna 60 and conductive body tissues. With the wirelesselectrode assembly 120 of FIG. 5, however, all implanted wirelesselectrode assemblies can be charged simultaneously with a burst of RFcurrent in antenna 60, and antenna and body tissue heating occurs onlyduring the time required for this single short burst. Each wirelesselectrode assembly 120 is addressed independently through its filterdevice 176 to trigger pacing. The transmitted trigger fields can be ofmuch smaller amplitude, and therefore lose much less energy to Ohmicheating, than the transmitted charging pulse.

Referring now to the process of delivering the wireless electrodeassemblies 120 to the heart wall tissue 35 as shown in FIGS. 6-8, theelectrode delivery system 100 may be operated to initially penetrate theheart wall tissue 35 with the guide wire instrument 140 before advancingthe electrode assembly 120 into the tissue 35. Such initial penetrationby the guide wire instrument 140 can facilitate the subsequentpenetration by the electrode assembly 120. As shown in FIG. 6, the guidesheath 110 is shown within a targeted heart chamber, and the deliverycatheter 130 may be advanced to an implantation site along theendocardium 33. As previously described in connection with FIGS. 2-3,the guide sheath 110 may be introduced via an incision in the patient'sneck and advanced through the venous system to the heart 30 (e.g.,though the superior vena cava and into the heart 30) or via an incisionin the patient's leg and advanced through one or more arteries to theheart 30 (e.g., through the femoral artery, around the aortic arch, andinto the heart 30). Also as previously described, the delivery catheter130 can be directed through the guide sheath 110 to the targeted heartchamber. The magnetic coupling device 150 may releasably retain theelectrode assembly 120 in the non-deployed position inside the distalportion 134 of the delivery catheter 130. In this embodiment, the distalsection 162 of the actuation member 160 is in a retracted position suchthat the shoulder 164 is separated from the centering mechanism 154 byat least a separation distance L.

Still referring to FIG. 6, when the delivery catheter 130 has beendirected to the targeted implantation site along the endocardium 33, thedistal tip portion 142 of the guide wire instrument 140 can be advanceddistally to penetrate through the endocardium and into the heart walltissue 35. As previously described, the guide wire instrument 140 mayinclude at least one sensor electrode 144 along its distal tip portion142 that is configured to sense local electrical activity (e.g., anelectrogram or the like) and to transmit a test stimulation signal(e.g., a pacing signal) at the implantation site. In thesecircumstances, the guide wire instrument 140 may be used to determine ifthe implantation site is suitable for receipt of an electrode assembly120 before the electrode assembly 120 is advanced into the heart walltissue 35. The sensor electrode 144 may be in electrical communicationwith an electrogram or ECG monitor system (e.g., outside the patient'sbody) or the like so that a physician may view the local electricalactivity in the heart wall tissue 35 into which the distal tip portion142 has penetrated. Optionally, a pulse generator device or the like maybe electrically connected to the proximal portion 148 (FIG. 3) of theguide wire instrument 140 so as to transmit test pacing signals to heartwall tissue 35 proximate to the sensor electrode 144.

Referring to FIG. 7, after the guide wire instrument 140 has penetratedinto the heart wall tissue 35, the actuation member 160 may be adjustedso as to force the electrode assembly 120 over the guide wire instrument140 and into the heart wall tissue 35. As previously in connection withFIGS. 2-3, a surgeon or other user may actuate a hand-operated triggerdevice 137 (FIG. 3) or the like disposed along the proximal portion 138of the delivery catheter 130 to adjust the position of the distalsection 162 of the actuation member 160. For example, the distal section162 of the actuation member 162 may abut the proximal surface 128 of theelectrode assembly 120 so that the actuation member 160 transmits aninsertion force to the electrode assembly 120 (in response to actuationof the trigger device 137 (FIG. 3)). Such an insertion force advancesthe electrode assembly 120 over the guide wire instrument 140 as theguide wire channel 122 slides over the distal tip portion 142. Also, aspreviously described, the tissue penetration surface 127 may engage tothe heart wall tissue 130 to open the tissue as the electrode assembly120 is advanced. The actuation member 160 may be pushed forward by adistance L (FIG. 6) before the shoulder 164 abuts the centeringmechanism 154. According, the depth of penetration of the electrodeassembly 120 is controlled by the limited distance to which theactuation member 160 may be adjusted while advancing the electrodeassembly 120. In other embodiments, the depth of penetration of theelectrode assembly 120 may be controlled or monitored using stopperdevices, depth markings along the trigger device 137 (FIG. 3), or thelike. Advancing the electrode assembly 120 into the heart wall tissue130 in such a controllable manner can reduce the likelihood of forcingthe electrode assembly 120 fully through the heart wall.

Referring to FIG. 8, after the electrode assembly 120 is advanced overthe guide wire instrument 140 to a selected depth into the heart walltissue 35, the guide wire instrument 140 and the actuation member 160may be withdrawn from the tissue 35. The opening in the endocardium 33through which the actuation member 160 was passed may substantiallyretract after the actuation member 160 is withdrawn, thereby embeddingthe electrode assembly 120 in the heart wall tissue 35. In someembodiments, the embedded electrode assembly 120 may be prompted totransmit a test stimulation pulse from the electrode surfaces 124 and126, which can verify the operability of the electrode assembly 120 inthe implantation site. The actuation member 160, the guide wireinstrument 140, and the delivery catheter 130 may be retracted from theguide sheath 110 while the guide sheath 110 maintains the delivery pathinto the targeted heart chamber. As previously described, if asubsequent electrode assembly 120 is to be delivery to the same heartchamber, a new electrode assembly 120 may be loaded into the samedelivery catheter 130 (or into a new delivery catheter 130 having asimilar construction) for delivery through the guide sheath 110 to a newimplantation site along the targeted heart chamber wall. Thus, thesubsequent electrode assembly 120 can be delivered to the targeted heartchamber without having to remove the guide sheath 110 from the heart 30,thereby reducing the likelihood of irritation or trauma to the atrialseptum, the heart valves, and other heart structures caused by repeatedinsertions of a sheath or catheter.

Referring now to FIGS. 9-10, in some embodiments, the electrode assembly120 may be advanced into the heart wall tissue 35 in a direction that isnon-perpendicular to the endocardial surface 33. For example, someembodiments of the guide wire instrument 240 may include a curvedsection 245 along the distal tip portion 242 so that the electrodeassembly follows a curved path as it is advanced into the heart walltissue 35. As shown in FIG. 9, some embodiments of an electrode deliverysystem 200 include a curved guide wire instrument 240 that is slidablyengageable with a wireless electrode assembly 120. As described inconnection with previous embodiments, the wireless electrode assembly120 may include a guide wire channel 122 that slidably engages the guidewire instrument 240 during advancement into the heart wall tissue 35.Similar to the previously described embodiments, the electrode assembly120 may be releasably retained in a delivery catheter 130 using amagnetic coupling device 150, and an actuation member 160 may beadjusted in a controlled manner to advance the electrode assembly 120over the guide wire instrument 240.

Still referring to FIG. 9, when the delivery catheter 130 has beendirected to the targeted implantation site along the endocardium 33, thedistal tip portion 242 of the guide wire instrument 240 can penetratethrough the endocardium 33 and into the heart wall tissue 35. Similar toprevious embodiments, the guide wire instrument 240 may include at leastone sensor electrode 244 along its distal tip portion 242 that isconfigured to sense local electrical activity (e.g., an electrogram orthe like) and to transmit a test stimulation signal (e.g., a pacingsignal) at the implantation site. The distal portion 242 of the guidewire instrument 240 may include at least one curved section 245 thatpermits the distal portion to penetrate a particular distance beforeturning and tunneling sideways into the heart wall tissue 35. The radiusof curvature, the stiffness of the curved section, and the shape of theremaining portions of the distal tip portion 242 may be selected basedat least in part upon the penetration resistance of the myocardiumencountered by the distal tip portion 242. In some embodiments, thecurved section 245 may be configured to provide the desired penetrationdepth and curvature into a desired tissue plane between the myocardialtissue fibers. In this embodiment, at least the curved section 245 ofthe distal tip portion 242 comprises an elastically deformable materialsuch as a shape memory material (e.g., Nitinol or the like) thatexhibits elasticity or super elasticity when used in the patient's body.The elastically deformable material the permits the curved section 245to be substantially straightened while passing through the channel inthe actuation member 160 (e.g., passed through the delivery catheter 130toward the heart chamber wall). Such an elastically deformable materialcan return to the desired curvature after being released from therestraint in the channel of the actuation member 160.

Referring to FIG. 10, after the guide wire instrument 240 has penetratedin the heart wall tissue 35 and curved in a path non-perpendicular tothe endocardial surface 33, the actuation member 160 can be adjusted toadvance the electrode assembly 120 over the guide wire 240 and into thetissue 35. As the actuation member 160 applies an insertion force to theelectrode assembly 120, the electrode assembly 120 may slidably engagethe distal tip portion 242 and penetrate along the curved path towardthe direction that is non-perpendicular to the endocardial surface. Insome circumstances, the distal section 162 of the actuation member 160may comprise a flexible material (e.g., a polymer shaft, a shaftcomprising metallic coils, or the like) so that it may advance over atleast a portion of the curved section 245. As previously described, theactuation member 160 may be controllably adjusted so that the electrodeassembly 120 is advanced a selected distance along the guide wireinstrument 240. In the embodiment shown in FIG. 10, the electrodeassembly 120 includes one or more barbs 129 that extend outward from thebody portion 125 when the electrode assembly 120 is deployed into theheart wall tissue 35. The barbs 129 may comprise a shape memory material(e.g., Nitinol or the like) that can flex into a non-deployedconfiguration (refer to FIG. 9) when the electrode assembly 120 isreleasably retained in the delivery catheter 130. The barbs 129 may bedeployed as fixation devices to maintain the orientation of theelectrode assembly 120 while the actuation member 160 and guide wireinstrument 240 are withdrawn from the tissue 35.

Referring to FIGS. 11-13, the distal tip portion 240 of the guide wireinstrument 240 may be configured to bend during insertion into the heartwall tissue 35 so as to provide a curved insertion path. For example, asshown in FIG. 11, the distal tip portion 249 may include a pointed tip249 that penetrates into the tissue 35 before a shape memory curvedsection (refer to section 245 in FIGS. 9-10) causes the distal tipportion to extend along a curved path in the heart wall tissue 35. Inaddition or in the alternative, a guide wire instrument 250 may beformed with a flattened tip 259 that can penetrate into the heart walltissue 35 but subsequently bends when more rigid tissue is encountered.Thus, in some circumstances, the guide wire instrument 250 may beadvanced into the heart wall tissue 35 and through the myocardium beforeencountering a more rigid portion of the epicardial layer. In responsethereto, the flattened tip 259 of the guide wire instrument 250 may flexso that the distal portion 252 of the guide wire instrument 250 extendsin a curved path through the heart wall tissue 35. In yet anotherembodiment, a guide wire instrument 260 may include a combination of apointed and flattened tip 269 that can penetrate into the heart walltissue 35 but subsequently bends when more rigid tissue is encountered.Such a guide wire instrument 250 or 260 with a bendable tipconfiguration may be used to form the curved path rather than thepreviously described shape memory curved section 245.

Referring now to FIGS. 14-15, some embodiments of a guide wireinstrument may include a fixation device along the distal tip portion sothat the guide wire instrument may be secured to the heart wall tissue35 during the advancement of the electrode assembly 120 into the tissue35. Such a fixation device can maintain the position of the guide wireinstrument and reduce the likelihood of the distal tip portion beingextended or retracted during the electrode assembly insertion process.For example, as shown in FIG. 14, some embodiments of a guide wireinstrument 270 may include a fixation device in the form of a helicaltine 279 extending from the distal tip portion 272. As such, the guidewire instrument 270 may be twisted as it penetrates into the heart walltissue 35 so that the distal tip portion 272 is “screwed into” the heartwall tissue 35. After the electrode assembly 120 is advanced into theselected implantation site, the guide wire instrument 270 may bewithdrawn by twisting the instrument in the opposite direction to“unscrew from” the heart wall tissue 35. In another example, as shown inFIG. 15, some embodiments of a guide wire instrument 280 may include afixation device in the form of an adjustable barbs 289 that extend froma non-deployed configuration to a deployed configuration. In theseembodiments, the adjustable barbs may be in a non-deployed configurationas the guide wire instrument 280 is passed through the delivery catheter130 toward the heart wall tissue 35. The adjustable barbs may expandoutward (e.g., away from the central guide wire axis) when no longerrestrained by the surrounding instruments.

Referring to FIGS. 16-17, some embodiments of an electrode deliverysystem may include a guide wire instrument having a detachable tipportion. As such, the detachable tip portion may remain engaged with theelectrode assembly 120 after it has been embedded in the heart walltissue 35.

As shown in FIG. 16, one embodiment of an electrode delivery system 300includes a delivery catheter 130 that can be directed through a guidesheath (not shown in FIG. 16) toward a targeted site along theendocardium 33. Similar to previously described embodiments, theelectrode delivery system 300 may include a magnetic coupling device 150to releasably retain the electrode assembly 120 in the delivery catheter130 and may include an actuation member 160 to advance the electrodeassembly 120 over the guide wire instrument 340. The guide wireinstrument may be detachable along mating portions 347 and 348 so thatthe detachable portion 342 remains with the electrode assembly 120 inthe heart wall tissue 35.

In operation of the electrode delivery system 300, the delivery catheter130 may be directed to a targeted site on the endocardium 33, and theguide wire instrument 340 may be inserted through the endocardium 33 andinto the heart wall tissue 35. The guide wire instrument 340 may includeadjustable barbs 349 extending from a distal tip so as to secure thedetachable portion 342 of the guide wire instrument 340 to the heartwall tissue 35. After the guide wire instrument has initiatedpenetration into the heart wall tissue 35, the actuation member 160 mayapply an insertion force to the electrode assembly 120 so that theelectrode assembly separates from the magnetic coupling device 150 andadvances along the guide wire instrument 340 to a controlled depth.Similar to previously described embodiments, the electrode assembly 120may include one or more barbs 129 that adjust to a deployedconfiguration so as to retain the position of the electrode assembly 120in the heart wall tissue 35. After the electrode assembly 120 isadvanced to into the heart wall tissue, the guide wire instrument 340may be detached along the mating portions 347 and 348 so that thedetachable portion 342 remains engaged with the electrode assembly 120,For example, the mating portions 347 and 348 may comprise mating tongueand groove sections that are separable when a torque is applied to theproximal end of the guide wire instrument 340 (similar to the proximalportion 148 shown in FIG. 3). Such a relative twisting action may causethe mating portions 347 and 348 to separate, thereby permitting theguide wire instrument 340 (along with the actuation member 160) to beretracted away from the heart chamber wall. The detachable tip portion342 of the guide wire instrument 340 may serve as an anchor to theelectrode assembly 120 embedded in the heart wall tissue 35. Forexample, the detachable tip portion 342 may reduce the likelihood ofmigration and changes in orientation of the electrode assembly 120 afterrepeated heart contractions.

Referring to FIG. 17, another embodiment of an electrode delivery system400 includes a guide wire instrument 440 having a detachable tip portion442 that is curved. In this embodiment, the electrode delivery system400 includes a delivery catheter 130 that can be directed through aguide sheath (not shown in FIG. 17) toward a targeted site along theendocardium 33. Similar to previously described embodiments, theelectrode delivery system 400 may include a magnetic coupling device 150to releasably retain the electrode assembly 120 in the delivery catheter130 and may include an actuation member 160 to advance the electrodeassembly 120 over the guide wire instrument 440. The guide wireinstrument 440 may be detachable along mating portions 447 and 448 sothat the detachable portion 442 remains with the electrode assembly 120in the heart wall tissue 35. Also, the guide wire instrument 440includes two curved sections 445 and 446 so that the guide wireinstrument 440 penetrates along a curved path in the heart wall tissue35.

In operation of the electrode delivery system 400, the delivery catheter130 may be directed to a targeted site on the endocardium 33, and theguide wire instrument 440 may be inserted through the endocardium 33 andinto the heart wall tissue 35. The curved sections 445 and 446 of theguide wire instrument 440 may cause the detachable tip portion 442 topenetrate through the endocardium 33 into the heart wall tissue 35 acertain depth before curving along a path that is non-perpendicular tothe endocardial surface 33 and then curve again in a path that returnstoward the endocardial surface 33. After the guide wire instrument 440has initiated penetration into the heart wall tissue 35, the actuationmember 160 may apply an insertion force to the electrode assembly 120 sothat the electrode assembly 120 separates from the magnetic couplingdevice 150 and advances along the guide wire instrument 440 for aselected advancement length. Similar to previously describedembodiments, the electrode assembly 120 may include one or more barbs129 that adjust to a deployed configuration so as to retain the positionof the electrode assembly 120 in the heart wall tissue 35. After theelectrode assembly 120 is advanced to into the heart wall tissue 35, theguide wire instrument 440 may be detached along the mating portions 447and 448 so that the detachable portion 442 remains engaged with theelectrode assembly 120. As such, the guide wire instrument 440 (alongwith the actuation member 160) can be retracted away from the heartchamber wall. The detachable tip portion 442 of the guide wireinstrument 440 may serve as an anchor to the electrode assembly 120embedded in the heart wall tissue 35. For example, the detachable tipportion 442 can maintain the orientation of the electrode assembly 120in the heart wall tissue 35 and the second curved sections 446 mayinhibit the electrode assembly 120 from forwardly migrating toward thedistal tip of the detachable portion 442.

Referring to FIGS. 18-19, some embodiments of an electrode deliverysystem 500 may include a detachable anchor mechanism 570 that engagesthe electrode assembly 120 after the guide wire instrument 540 has beenwithdrawn from the heart wall tissue 35. In this embodiment, theelectrode delivery system 500 includes a delivery catheter 130 that canbe directed through a guide sheath (not shown in FIGS. 18-19) toward atargeted site along the endocardium 33. Similar to previously describedembodiments, the electrode delivery system 500 may include a magneticcoupling device 150 to releasably retain the electrode assembly 120 inthe delivery catheter 130 and may include an actuation member 160 toadvance the electrode assembly 120 over the guide wire instrument 540that the detachable anchor mechanism 570. The guide wire instrument 540may be slidably engaged with the detachable anchor mechanism 570, andthe wireless electrode assembly may include a guide wire channel 522 soas to slide over the guide wire instrument 540 and the detachable anchormechanism 570. The anchor mechanism 570 can be detachable along matingportions 577 and 578 so that the detachable distal portion 572 remainswith the electrode assembly 120 in the heart wall tissue 35.

In operation of the electrode delivery system 500, the delivery catheter130 may be directed to a targeted site on the endocardium 33, and theguide wire instrument 540 may be inserted through the endocardium 33 andinto the heart wall tissue 35 (refer, for example, to FIG. 18). Afterthe guide wire instrument 540 has penetrated into the heart wall tissue35, the anchor mechanism 570 may be advanced over the guide wireinstrument 540 and into the heart wall tissue 35 to further dilate theopening formed in the endocardium 33 (refer, for example, to FIG. 18).The anchor mechanism 570 may include one or more adjustable barbs 579extending from a distal tip portion so as to secure the anchor mechanism570 to the heart wall tissue 35. After the guide wire instrument 540 andthe anchor mechanism 570 have initiated penetration into the heart walltissue 35, the actuation member 160 may apply an insertion force to theelectrode assembly 120 so that the electrode assembly 120 separates fromthe magnetic coupling device 150 and advances over the anchor mechanism570 for a selected advancement length. When the electrode assembly 120is advanced to into the heart wall tissue 35, the anchor mechanism 570may be detached along the mating portions 577 and 578 so that thedetachable portion 572 remains engaged with the electrode assembly 120.In these circumstances, the anchor mechanism 570, the guide wireinstrument 540, and the actuation member 160 can be retracted away fromthe heart chamber wall (refer, for example, to FIG. 19). Optionally, theguide wire instrument 540 may be withdrawn from the heart wall tissuebefore the electrode assembly 120 is advanced over the anchor mechanism570.

The detachable distal portion 572 of the anchor mechanism 570 may serveas an anchor to the electrode assembly 120 embedded in the heart walltissue 35. In this embodiment shown in FIG. 19, the mating portion 578is bent during the detachment process (or elastically biased) so as toengage an inner conical surface 528 of the electrode assembly 120. Suchan engagement reduces the likelihood of the electrode assembly 120migrating proximally away from the adjustable barbs 579 at the distaltip of the detachable portion 572. Accordingly, the detachable distalportion 572 may serve to maintain the orientation of the electrodeassembly 120 in the heart wall tissue 35.

Referring now to FIG. 20, some embodiments of an electrode deliverysystem 600 may include a guide wire instrument 640 having a detachmenttip portion 642 configured to engage an inner surface of the electrodeassembly 120 when implanted in the heart wall tissue 35. In thisembodiment, the electrode delivery system 600 includes a deliverycatheter 130 that can be directed through a guide sheath (not shown inFIG. 20) toward a targeted site along the endocardium 33. Similar topreviously described embodiments, the electrode delivery system 600 mayinclude a magnetic coupling device 150 (not shown in FIG. 20) toreleasably retain the electrode assembly 120 in the delivery catheter130 and may include an actuation member 160 to advance the electrodeassembly 120 over the guide wire instrument 640. The guide wireinstrument 640 may be detachable along mating portions 647 and 648 sothat the detachable portion 642 remains with the electrode assembly 120in the heart wall tissue 35. Also, the guide wire instrument 640 caninclude one or more adjustable stoppers 646 to engage one or more innersurfaces of the electrode assembly 120.

In operation of the electrode delivery system 600, the delivery catheter130 may be directed to a targeted site on the endocardium 33, and theguide wire instrument 640 may be inserted through the endocardium 33 andinto the heart wall tissue 35. The guide wire instrument includes one ormore adjustable barbs 649 that extend from the distal tip to secure thedetachable tip portion 642 to the heart tissue. The adjustable barbs 649and the adjustable stoppers 646 may be flexed into a non-deployedconfiguration (e.g., pressed against the guide wire body) when the guidewire instrument is passed through a central channel of the actuationmember 160. As the detachable tip portion 642 is inserted into the heartwall tissue, the adjustable barbs 649 and the adjustable stoppers mayextend outwardly to a deployed configuration (as shown, for example, inFIG. 20). After the guide wire instrument 640 has initiated penetrationinto the heart wall tissue 35, the actuation member 160 may apply aninsertion force to the electrode assembly 120 so that the electrodeassembly 120 separates from the magnetic coupling device 150 andadvances along the guide wire instrument 640 for a selected advancementlength. The electrode assembly 120 may advance in a distal directionover the stoppers 646 during the insertion process (e.g., the stoppers646 may partially flex inwardly to permit passage of the electrodeassembly 120 in the distal direction). When the electrode assembly isadvanced to the selected advancement length, the stoppers 646 may engageone or more inner surfaces 626 of the electrode assembly 120, which canreduce the likelihood of the electrode assembly 120 migrating proximallyaway from the adjustable barbs 649 at the distal tip of the detachableportion 642.

After the electrode assembly 120 is advanced into the heart wall tissue35, the guide wire instrument 640 may be detached along the matingportions 647 and 648 so that the detachable portion 642 remains engagedwith the electrode assembly 120. As such, the guide wire instrument 640(along with the actuation member 160) can be retracted away from theheart chamber wall. The detachable tip portion 642 of the guide wireinstrument 640 may serve as an anchor to the electrode assembly 120embedded in the heart wall tissue 35. For instance, the detachable tipportion 642 can maintain the orientation of the electrode assembly 120in the heart wall tissue 35.

Referring to FIGS. 21-25, some embodiments of an electrode deliverysystem may include a delivery catheter that is configured to releasablysecure to the heart wall tissue 35 during the implantation process. Sucha releasable attachment to the heart chamber wall permits the deliverycatheter to maintain its position adjacent the targeted implantationsite. After the electrode assembly 120 is inserted into the heart walltissue 35, the delivery catheter may be released from the heart chamberwall and withdrawn into the guide sheath 110.

As shown in FIG. 21, some embodiments of an electrode delivery system700 may include a delivery catheter 730 having a fixation device toreleasably engage the heart wall tissue 35. In this embodiment, thedelivery catheter 730 includes a fixation device in the form of ahelical tine 735 that extends distally from the tip of the deliverycatheter 730. The electrode delivery system 700 includes a guide sheath110 that slidably receives the delivery catheter 730 so that thedelivery catheter can be directed toward a targeted site along theendocardium 33. Similar to previously described embodiments, theelectrode delivery system 700 may include a magnetic coupling device 150to releasably retain the electrode assembly 120 (not shown in FIG. 21)in the delivery catheter 730 and may include an actuation member 160(not shown in FIG. 21) to advance the electrode assembly 120 over theguide wire instrument 140.

In operation, the delivery catheter 730 may be twisted as it approachesthe endocardium 33 so that the helical tine 735 is “screwed into” theheart wall tissue 35. After the delivery catheter is secured to theheart wall tissue, the guide wire instrument 140 can penetrate into theheart wall tissue 35 to prepare the insertion path for the electrodeassembly 120 (not shown in FIG. 21). When the guide wire instrument haspenetrated into the heart wall tissue 35, the electrode assembly 120 maybe advanced over the guide wire instrument 140, as described in previousembodiments, for example, in connection with FIGS. 6-8. After insertionof the electrode assembly 120, the guide wire instrument 140 and theactuation member 160 (not shown in FIG. 21) can be retracted into thedelivery catheter 730, and the helical tine 735 of the delivery catheter730 can be “unscrewed” or otherwise released from the heart wall tissue35. It should be understood that, in some embodiments, the electrodedelivery system 700 may include the delivery catheter 730 to releasablysecure with the heart wall tissue 35 and may include one or morealternative guide wire instruments, such as those guide wire embodimentspreviously described in connection with FIGS. 9-17 and 20.

Referring to FIGS. 22-25, some embodiments of an electrode deliverysystem 800 may include a delivery catheter 830 having at least oneadjustable fixation device to releasably engage the heart wall tissue35. In this embodiment, the delivery catheter 830 includes adjustablefixation devices in the form of adjustable barbs 835 that can bedistally extended to curl outwardly from the tip of the deliverycatheter 830. The electrode delivery system 800 includes a guide sheath110 that slidably receives the delivery catheter 830 so that thedelivery catheter 830 can be directed toward a targeted site along theendocardium 33. Similar to previously described embodiments, theelectrode delivery system 800 may include a magnetic coupling device 150to releasably retain the electrode assembly 120 (not shown in FIGS.22-25) in the delivery catheter 830 and may include an actuation member160 (not shown in FIGS. 22-25) to advance the electrode assembly 120over the guide wire instrument 140.

In operation, the adjustable barbs 835 may be retracted in anon-deployed configuration as the delivery catheter 830 approaches theendocardium 33 (refer, for example, to FIGS. 23-24). The adjustablebarbs 835 may be coupled with a slider ring 836 that is extended andretracted by a threaded ring 837. The threaded ring 837 may be engagedby mating threads 838 along an inner distal surface of the deliverycatheter 830. As such, an actuation shaft 839 that is fixedly attachedto the threaded ring 837 may be twisted so as to turn the threaded ring837 relative to the threads 838. Such a turning motion causes thethreaded ring 837 to push (or pull) the slider ring 836 between thenon-deployed configuration (FIG. 24) and the deployed configuration(FIG. 25). As the slider ring 836 is moved to the distal position (FIG.25), the adjustable barbs 835 may extend distally from the deliverycatheter 830 to engage the heart wall tissue 35. In this embodiment, theadjustable barbs 835 may comprise a shape memory material (e.g., Nitinolor the like) so that the barbs 835 curl outwardly away from the distaltip of the delivery catheter 830 when disposed in the deployedconfiguration. Such an embodiment permits the barbs to be flexed into agenerally non-curved, longitudinal orientation when disposed in thenon-deployed configuration (as shown, for example, in FIG. 24).

After the delivery catheter 830 is secured to the heart wall tissue 35,the guide wire instrument 140 can penetrate into the heart wall tissue35, as shown in FIG. 22, to prepare the insertion path for the electrodeassembly 120 (the electrode assembly 120 is not shown in FIG. 22). Whenthe guide wire instrument has penetrated into the heart wall tissue 35,the electrode assembly 120 may be advanced over the guide wireinstrument 140, as described in previous embodiments, for example, inconnection with FIGS. 6-8. After insertion of the electrode assembly120, the guide wire instrument 140 and the actuation member 160 (notshown in FIGS. 22-25) can be retracted into the delivery catheter 830,and the adjustable barbs 835 of the delivery catheter 830 can bereleased from the heart wall tissue 35. It should be understood that, insome embodiments, the electrode delivery system 800 may include thedelivery catheter 830 to releasably secure with the heart wall tissue 35and may include one or more alternative guide wire instruments, such asthose guide wire embodiments previously described in connection withFIGS. 9-17 and 20.

Accordingly, in these embodiments, the delivery catheter 730 or 830 maybe configured to releasably secured to the heart wall tissue 35 duringthe implantation process. Such a releasable attachment to the heartchamber wall permits the delivery catheter 730 or 830 to maintain itsposition adjacent the targeted implantation site. After the electrodeassembly 120 is inserted into the heart wall tissue 35, the deliverycatheter 730 or 830 may be released from the heart chamber wall andwithdrawn into the guide sheath.

It should be understood from the description here that the deliverysystem 100 can be employed to deliver electrode assemblies 120 tolocations in the body other than the human 30. For example, the guidesheath 110 and delivery catheter 130 can be used to implant one orelectrode assemblies 120 to tissue in the digestive tract (e.g., stomachtissue) for electrical stimulation treatment of digestive conditions orobesity. In another example, the guide sheath 110 and delivery catheter130 can be used to implant one or electrode assemblies 120 to tissue inthe urinary tract (e.g., urinary sphincter) for electrical stimulationtreatment of incontinence or other urinary conditions.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A wireless pacing electrode delivery system,comprising: a guide sheath including a distal end and a lumen extendingto the distal end; and an intravascularly-deliverable medical devicepositionable within the lumen of the guide sheath, theintravascularly-deliverable medical device including a fixation deviceconfigured to engage heart wall tissue, the intravascularly-deliverablemedical device configured to be advanced distal of the distal end of theguide sheath to engage the hear wall tissue; wherein the fixation deviceincludes four tines attached to and extending distally from a ring, thefour tines having a non-deployed configuration and a deployedconfiguration, wherein in the non-deployed configuration the four tinespoint distally toward the heart wall tissue to pierce into the heartwall tissue, and wherein the four tines are biased to curl outwardly tothe deployed configuration when unconstrained to engage the heart walltissue.
 2. The system of claim 1, wherein the four tines extend in alongitudinal orientation when constrained in the non-deployedconfiguration.
 3. The system of claim 1, wherein the four tines contactan inner wall of the delivery system when constrained in thenon-deployed configuration.
 4. The system of claim 1, wherein the fourtines extend distal of the distal end of the guide sheath whenpositioned in the deployed configuration.
 5. The system of claim 1,wherein the four tines are formed of a shape memory material.
 6. Thesystem of claim 5, wherein the shape memory material is nitinol.
 7. Thesystem of claim 1, wherein the four tines extend from a distal end ofthe intravascularly-deliverable medical device in the deployedconfiguration.
 8. The system of claim 1, further comprising an actuatorconfigured to deploy the four tines from the non-deployed configurationto the deployed configuration.
 9. The system of claim 8, wherein thefour tines are configured to moved linearly in a longitudinal directionin response to actuation of the actuator.
 10. A wireless pacingelectrode delivery system, comprising: a guide sheath including a lumen;and an intravascularly-deliverable medical device positionable withinthe lumen of the guide sheath and configured to be advanced out of adistal opening of the guide sheath to engage heart wall tissue; theintravascularly-deliverable medical device including a fixation deviceincluding four tines attached to and extending distally from a ring;wherein the four tines are constrained in a non-deployed configurationwhen positioned within the lumen of the guide sheath and biased toward adeployed configuration when unconstrained, wherein the four tines arecurled outwardly in the deployed configuration; wherein the four tinesare configured to pierce into the heart wall tissue without penetratingentirely through the heart wall tissue to an opposite face of the heartwall tissue to engage the heart wall tissue when in the deployedconfiguration.
 11. The system of claim 10, wherein the four tines extendin a longitudinal orientation when constrained in the non-deployedconfiguration.
 12. The system of claim 10, wherein the four tinescontact an inner wall of the delivery system when constrained in thenon-deployed configuration.
 13. The system of claim 10, wherein the fourtines extend distal of the distal end of the guide sheath whenpositioned in the deployed configuration.
 14. The system of claim 10,wherein the four tines are formed of a shape memory material.
 15. Thesystem of claim 14, wherein the shape memory material is nitinol. 16.The system of claim 10, wherein the four tines extend from a distal endof the intravascularly-deliverable medical device in the deployedconfiguration.
 17. The system of claim 10, further comprising anactuator configured to deploy the four tines from the non-deployedconfiguration to the deployed configuration.
 18. The system of claim 17,wherein the four tines are configured to moved linearly in alongitudinal direction in response to actuation of the actuator.